Chem 110 Reci Week 7 Kinetics II

Chem 110 Reci – Week 7 – Kinetics II

More Linear Regression/Integrated Rate Law Examples:

1. The hydrolysis of table sugar (sucrose) occurs by the following overall reaction:

C12H22O11(s) + H2O(l) C6H12O6(aq, glucose) + C6H12O6(aq, fructose)

A nutritional biochemist studes the kinetics of the process and obtains the following data:

a) use the data to determine the rate constant and the half-life of the reaction.

b) How long does it take to hydrolyze 75% of the sucrose?

2. In a first order decomposition reaction, 50.0% of a compounds decomposes in 10.5 min.

a) What is the rate constant of the reaction?

b) How long does it take for 75.0% of the compound to decompose?

3. A decomposition reaction has a rate constant of 0.0012 yr-1.

a) What is the half-life of the reaction?

b) How long does it take for the reactant to reach 12.5% of it’s original value?

4. A biochemist studying the breakdown in soil of the insecticide DDT finds that it decomposes by a first-order reaction with a half-life of 12 yr. How long does it take DDT to decompose from 275 ppbm to 10 ppbm in a soil sample?

5. Aspirin in broken down in the body by a first-order process. The half-life of aspirin in elderly humans is 3.7 hr.

a) How much aspirin remains in the bloodstream from a 160-mg dose after 24 hours?

b) In young humans, the half-life is 2.4 hr. How much aspirin remains in a young person 24 hours after the same dose?

More Initial Rate Examples:

1. a) Give the individual reaction order for each substance and the overall reaction order for the following rate laws:
i) rate = k[BrO3-][Br-][H+]2, ii)

b) By what factor does rate law i) change if:

i) the [Br-] is halved, ii) the [H+] is quadrupled

c) By what factor does rate law ii) change if:

i) the [O3] is doubled, ii) the [O2] is doubled

2. For the reaction

4A(g) + 3B(g)  2C(g)

the following data were obtained at constant temperature:

a) What is the order with respect to each reactant?

b) Write the rate law.

c) Calculate the rate constant.

3. For the reaction

A(g) + B(g) + C(g)  D(g)

the following data were obtained at constant temperature:

a) What is the order with respect to each reactant?

b) Write the rate law.

c) Calculate the rate constant.

4. Give the units of the rate constant for the following orders:

a) firstb) fifthc) thirdd) 5/2

5. Give the overall reaction order that corresponds to rate constants with the following units:

a) mol/L*sb) yr-1c) (mol/L)1/2*s-1d)(mol/L)-5/2*min-1

Mechanism Examples:

1. The proposed mechanism for a reaction is

1) A(g) + B(g) X(g)fast

2) X(g) + C(g) Y(g)slow

3) Y(g) D(g)fast

a) What is the overall equation?

b) Identify any intermediates.

c) what is the molecularity for each step?

d) If the mechanism instead were A(g) + B(g) + C(g)  D(g), would this be consistent with the rate law rate = k[A][B][C]?

2. In a study of nitrosyl halides, a chemist proposes the following mechanism for the synthesis of nitrosyl bromide:

NO(g) + Br2(g) NOBr2(g)fast

NOBr2(g) + NO(g) 2NOBr(g)slow

If the rate law for this reaction is rate = k[NO]2[Br], is the proposed mechanism valid?

3. The rate law for 2NO(g) + O2(g) 2NO2(g) is rate = k[NO]2[O2]. The following mechanisms have been proposed:

I.2NO(g) + O2(g) 2NO2(g)

II.2NO(g) N2O2(g)

N2O2(g) + O2(g) 2NO2(g)

III.2NO(g) N2(g) + O2(g)

N2(g) + 2O2(g) 2NO2(g)

a) which of these mechanisms is consistent with the rate law?

b) which is the most reasonable chemically?

Extra Practice:

1. Consider the following general reaction and data:

2A + 2B + C  D + 3E

a) What is the reaction order with respect to each reactant?

b) Calculate the rate constant.

c) Write the rate law for this reaction.

d) Express the rate in terms of changes in concentration with time for each of the components.

2. Is each of these statements true or false?

a) At a given temperature, all molecules posses the same kinetic energy.

b) Halving the pressure of a gaseous reaction doubles the reaction rate.

c) If reactant molecules collide with greater energy than the activation energy, they change into product molecules.

d) The rate of a reaction increases as a reaction proceeds.

e) Exothermic reactions always have higher rates than endothermic ones.

f) The initial rate of a reaction is its maximum rate.

g) A bimolecular reaction is generally twice as fast as a Unimolecular reaction.

h) The molecularity of an elementary reaction is proportional to the molecular complexity of the reactants.